Apparatus and method for controlling picture inversion of a liquid crystal display

ABSTRACT

An apparatus and related method for controlling picture inversion of an LCD, determining states of vertical and horizontal sync signals. The determined states are used to insert appropriate delay periods so as to allow picture inversion to take place only when the video signal is in a section of displaying no image, thereby eliminating a noise bar that is displayed during the picture inversion operation.

BACKGROUND OF THE INVENTION

A. Field of the Invention

The present invention relates to an apparatus and method for controllingpicture inversion of a liquid crystal display (hereinafter referred toas “LCD”).

B. Description of the Prior Art

A conventional LCD includes, as shown in FIG. 1, a video processor 1 forprocessing an externally-supplied signal to provide a mixed videosignal, and a signal processor 2 for receiving the mixed video signalfrom video processor 1 to provide a composite sync signal with avertical sync signal and a horizontal sync signal and a signal withoutthe sync signals. In addition, a sync signal generator 3 receives thecomposite sync signal from signal processor 2 and a control signal froma controller 5 to provide another new sync signal by means of a syncsignal supplied from an internal sync signal generating device, andcontroller 5 provides control signals to sync signal generator 3 and anLCD part 6 responsive to a key signal supplied from a key input part 4.Also, LCD part 6 receives R, G, B video signal from signal processor 2and the sync signal from sync signal generator 3 to display an image inaccordance with the control signal from controller 5.

In the conventional LCD formed as described above, as shown in FIG. 1,once the externally-supplied signal is received into video processor 1to provide the mixed video signal, signal processor 2 receives the mixedvideo signal from video processor 1 to separate the composite syncsignal having the vertical sync signal and horizontal sync signal andsupply it to sync signal generator 3 while supplying the other compositesync signal to LCD part 6.

At this time, sync signal generator 3 receives the composite sync signalsupplied from signal processor 2 to supply the new sync signal to signalprocessor 2 and LCD part 6 in accordance with the control signal fromcontroller 5. Simultaneously, the sync signal generator 3 supplies thecontrol signal to LCD part 6.

When the new sync signal supplied from sync signal generator 3 isreceived into signal processor 2, signal processor 2 synchronizes the R,G, B signal with the new sync signal from sync signal generator 3 tosupply the resultant signal to LCD part 6.

After the R, G, B signal from signal processor 2 and various controlsignals from sync signal generator 3 are supplied to LCD part 6 in theforegoing manner, the normal image is displayed on LCD part 6 inaccordance with the control signal from controller 5.

If a picture inversion signal is provided from key input part 4 whilethe normal image is displayed on LCD part 6, controller 5 receives thepicture inversion signal from key input part 4 to supply it to syncsignal generator 3. Following this, sync signal generator 3 changes thecontrol signal to correspond to the picture inversion in accordance withthe received picture inversion signal to supply the changed signal toLCD part 6. By this operation, LCD part 6 inverts thecurrently-displayed image in accordance with the picture inversioncontrol signal supplied from controller 5.

FIG. 2 shows timing charts of respective signals in the conventionalLCD. Referring to FIG. 2, (a) shows vertical sync signals; (b)horizontal sync signals; (c) picture inversion signal; and (d) pictureinversion control signal.

In other words, if the picture inversion signal (c), as shown in FIG. 2,is provided from key input part 4 when the mixed video signal suppliedform video processor 1 includes the vertical sync signal (a) andhorizontal sync signal (b), controller 5 receives the picture inversionsignal (c) during a prescribed time period Δt1 and provides the pictureinversion control signal (d) within a prescribed time period Δt2.

FIG. 3 illustrates pixels in the vertical axis and horizontal syncsignals of the LCD. In case of the NTSC, the image is displayed suchthat the actually-displayed video signals on LCD part 6 are the 15thhorizontal to the 248th horizontal sync signal when the vertical axispixels number approximately 234. The image is not displayed on LCD part6 at the horizontal sync signals in the sections H1 to H14 and H248 toH263.

The picture inversion is attained when the picture inversion signal isreceived into the displayed image in case that the time (obtained byΔt1+Δt2 from the vertical sync signal) taken for providing the pictureinversion control signal from controller 5 in response to the pictureinversion signal from key input part 4 exists within the section fromH15 to H248. However, an arbitrary signal, one other than the originalvideo signal, is displayed on the LCD part during the time (ofapproximately 2H to 5H) for executing the picture inversion. Thus, theconventional LCD heretofore has a problem of producing a severe noise onthe LCD part.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide anapparatus and method for controlling picture inversion of an LCD, toeliminate a noise generated on the LCD part during the picture inversionoperator.

Additional objects and advantages of the invention will be set forth inpart in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention will be realized and attained bymeans of the elements and combinations particularly pointed out in theappended claims.

To achieve the objects and in accordance with the purposes of theinvention, as embodied and broadly described herein, the inventioncomprises a signal detector for detecting a sync signal from a videosignal and a controller for providing a picture inversion control signalto selectively allow the video signal to invertedly display based on theresult of the detection of the signal detector and based on a pictureinversion input.

In another aspect, the invention includes a method for controllingpicture inversion of a liquid crystal display which comprises detectinga sync signal from a video signal in response to a picture inversioninput, determining whether video image is displayed on the liquidcrystal display or not, and selectively controlling a picture inversionoperation in accordance with the result of the detection anddetermination.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a structure of a conventional LCD.

FIG. 2 shows timing charts of respective signals in the conventionalLCD.

FIG. 3 is a view showing a relation between vertical axis pixels andhorizontal sync signals of an LCD.

FIG. 4 is a block diagram showing an apparatus for controlling pictureinversion of an LCD according to an embodiment of the present invention.

FIG. 5 is a flowchart showing a method for controlling picture inversionof the LCD according to an embodiment of the present invention.

FIG. 6 shows another embodiment of the apparatus for controlling pictureinversion of the LCD according to the present invention.

FIG. 7 shows timing charts of respective signals in the LCD according toan embodiment of the present invention.

FIG. 8 shows waveforms respectively showing the sections of the verticalsync signal and horizontal signal on the LCD according to an embodimentof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

To begin with, an apparatus for controlling picture inversion of an LCDaccording to the present invention, as shown in FIG. 4, includes a videoprocessor 11 for processing an externally-supplied signal to provide amixed video signal, and a signal processor 12 for receiving the mixedvideo signal from video processor 11 to provide a composite sync signalhaving a vertical sync signal and a horizontal sync signal and a signalhaving no sync signals. Also, a sync signal generator 13 receives thecomposite sync signal supplied from signal processor 12 and a controlsignal from a controller 16 to provide a new sync signal. A sync signaldetector 14 detects the vertical sync signal and horizontal sync signalfrom the mixed video signal output from video processor 11 to count thevertical sync signals by “1” and “2” and horizontal sections from H1 toH525 in terms of the horizontal sync signal, thereby providing theresult to controller 16. Here, controller 16 receives the vertical syncsignal and horizontal sync signal form sync signal detector 14 andreceives a picture inversion signal from a key input part 15 forproviding a picture inversion control signal to invertedly display avideo signal for liquid crystal by determining a section withoutinvolving the video signal for liquid crystal. Additionally, LCD part 17displays the image in accordance with the control signal from controller16 when the R, G, B signal from signal processor 12 and control signalfrom sync signal generator 13 are supplied thereto.

Hereinbelow, an operation of the present invention constructed as abovewill be described in detail with reference to FIG. 4.

Video processor 11 receives the externally-supplied signal to providethe mixed video signal to signal processor 12 and sync signal detector14. Signal processor 12 receives the mixed video signal from videoprocessor 11 to separate the composite sync signal into the verticalsync signal and horizontal sync signal and another composite signalwithout the sync signals, thereby providing the composite signal withthe sync signals to sync signal generator 13 and providing the compositesignal without the sync signals to LCD part 17.

At this time, sync signal generator 13 receives the composite syncsignal form signal processor 12 to supply the new sync signal to signalprocessor 12 in accordance with the sync signal supplied from theinternal sync signal generating device by means of the control signalfrom controller 16. At the same time, the control signal required in LCDpart 17 is supplied to LCD part 17 from sync signal generator 13.

Upon the receipt of new sync signal into signal processor 12 from syncsignal generator 13, signal processor 12 synchronizes the R, G, B signalwith the new sync signal from sync signal generator 13 to supply theresultant signal to LCD part 17.

When the R, G, B sync signal from signal processor 12 and variouscontrol signals from sync signal generator 13 are received into LCD part17, the normal image is displayed on LCD part 17 by means of the controlsignal from controller 16.

When the normal pictorial image is displayed on LCD part 17, sync signalgenerator 14 receives the mixed video signal from video processor 11 todetect the vertical sync signal and horizontal sync, thereby providingthe detected signals to controller 16.

A method for controlling picture inversion according to the presentinvention will now be described with reference to FIG. 5.

First, in step S101, signal processor 12 receives the mixed video signalfrom video processor 11 to judge whether the vertical sync signal asshown in FIG. 7A is indicated or not. When it is decided that thevertical sync signal is included, the program proceeds to step S102.Whereas, it proceeds to step S105 when it decides that no vertical syncsignal is included.

Thereafter, in step S102, the new sync signal is provided by adding “1”to the current vertical sync signal. In step S103, it is judged whetherthe new vertical sync signal is of an even number or not. When the newvertical sync signal is decided as of the even number, it proceeds tostep S104. Whereas, if the new vertical sync signal is of the oddnumber, it proceeds to step S105.

Then, in step S104, the horizontal sync signal is set to zero. In stepS105, if the vertical sync signal is of the odd number or the compositesync signal includes no vertical sync signal, it is judged whether thehorizontal sync signal is included or not. When it is decided that thehorizontal sync signal is included, the program proceeds to step S106.If the horizontal sync signal is not included, step S105 is repeatedlyperformed until the horizontal sync signal is detected.

In step S106, if the composite sync signal includes the horizontal syncsignal (b), as shown in FIG. 7, the new horizontal sync signal is formedby adding “1” to the current horizontal sync signal to be supplied tocontroller 16.

After this, in step S107, it is judged whether the picture inversionsignal (c), as shown in FIG. 7, is received from key input part 15, ornot when the new horizontal sync signal is supplied into controller 16.When it is decided that the picture inversion signal is received, itproceeds to step S108. If not, it proceeds to step S112, therebygenerating a “LOW” picture inversion control signal and maintaining thenormal pictorial image.

When the picture inversion signal is received, in step S108, it isdetermined whether the current horizontal sync signal is equal to orless than 8. If so, it proceeds to step S111, thereby generating a“HIGH” picture inversion control signal. If not, it proceeds to stepS109.

Once it is determined that the horizontal sync signal is greater than 8,it is further determined whether the horizontal sync signal falls withinthe section from 251 to 272 in step S109. If so, it proceeds to stepS111, thereby generating a “HIGH” picture inversion control signal. Ifnot, it proceeds to step S110.

In step S110, it is determined whether the horizontal sync signal isgreater than or equal to 514. If so, it proceeds to S111, therebygenerating a “HIGH” picture inversion control signal. If not, itproceeds to step S112, thereby generating a “LOW” picture inversioncontrol signal.

When the horizontal sync signal is less than or equal to 8, greater thanor equal to 251 and less than or equal to 272, or greater than or equalto 514 in step S111, controller 16 provides a high signal which is thepicture inversion control signal (d) (after elapsing a time periodobtained by Δt1+Δt2+Δt3 from the vertical sync signal) as shown in FIG.7 so as to execute the picture inversion on LCD part 17.

On the other hand, in step S112, when step S107 decides that there is nopicture inversion signal input or the horizontal sync signal is lessthan 514 in step S110, controller 16 provide a low signal formaintaining the normal image on LCD part 17.

In step S113, sync signal detector 14 judges whether the section of thecurrent horizontal sync signal is 525 or not. When the section of thecurrent horizontal sync signal is decided as 525, it proceeds to stepS114. If the section of the current horizontal sync signal is not 525,it proceeds to step S101 to repeatedly carry out the above-describedsteps.

In step S114, the section of the current horizontal sync signal is setto zero and the program is returned to step S101, thereby repeatedlycarrying out the foregoing steps.

More specifically, once the picture inversion signal is supplied fromkey input part 15 when the normal pictorial image is displayed on LCDpart 17, the picture inversion is performed with respect to thehorizontal sync signal (b), as shown in FIG. 8, in the sections of 1 to8, 251 to 272 and 514 to 525 while section 1 of the horizontal syncsignal (b) is synchronized with the odd field of the vertical syncsignal (a), as shown in FIG. 8. Thus, no noise is displayed on LCD part17 during the picture inversion operation.

The sections of the horizontal sync signal and vertical sync signal andassociated control time are described herein by assuming that the pixelsof LCD numbering 234 in the vertical axis is used as a reference. Whenthe pixel number in the vertical axis is changed into 240 or 480,adjustments can easily be made since there is a correlation with the 525horizontal sync signals (625 for the PAL) within one period of thevertical sync signal of the video signal.

FIG. 6 shows another embodiment of the apparatus for controlling pictureinversion of the LCD according to the present invention, which includesa video processor 11 for processing an externally-supplied signal toprovide a mixed video signal. A signal processor 12 receives the mixedvideo signal from video processor 11 to provide a composite sync signalhaving a vertical sync signal and a horizontal sync signal and a signalhaving no sync signals. Also included as parts are a sync signaldetector 14 for receiving the mixed video signal from video processor 11to detect the vertical sync signal and horizontal sync signal, and acontroller 16 for receiving the sync signals detected in sync signaldetector to discriminate a section without involving a video signal forliquid crystal, thereby providing a control signal that allows the videosignal for liquid crystal to be invertedly displayed in the sectionwithout involving the video signal for liquid crystal. Here, a referencenumeral 15 denotes a key input part; and 17, an LCD part.

In describing the operation and effect of another embodiment of theapparatus for controlling picture inversion of the LCD according to thepresent invention formed as above, as shown in FIG. 6, once theexternally-supplied signal is received into video processor 11 toprovide the mixed video signal, signal processor 12 receives the mixedvideo signal from video processor 11. Then, signal processor 11separates the composite sync signal having the vertical sync signal andhorizontal sync signal to provide the video signal to LCD part 17.

At this time, sync signal detector 14 receives the mixed video signal toseparately detect the sync signals and provide the detected signals tocontroller 16. Upon the receipt of the sync signals detected in syncsignal detector 14, controller 16 determines the section withoutinvolving the video signal for liquid crystal to provide the pictureinversion control signal so as to invertedly display the video signalfor liquid crystal in the section without involving the video signal forliquid crystal. By doing so, the noise is not displayed when the pictureof the video signal provided from signal processor 12 is invertedlydisplayed on LCD part 17 in accordance with the picture inversioncontrol signal.

As described above, when the picture is inverted during displaying theimage on the LCD part, the states of the vertical and horizontal syncsignals are determined to provide no inversion control signal in thesection of displaying the image on the LCD part but provide theinversion control signal in the section of displaying no image with theconsequence of eliminating the noise displayed on the LCD part duringthe picture inversion operation. As the result, the apparatus and methodfor controlling the picture inversion according to the present inventionare effective in enhancing reliability of the LCD.

While the present invention has been particularly shown and describedwith reference to particular embodiment thereof, it will be understoodby those skilled in the art that various changes in form and details maybe effected therein without departing from the spirit and scope of theinvention as defined by the appended claims.

1. An apparatus for controlling picture inversion of a liquid crystaldisplay, comprising: a signal detector for detecting a sync signal froma video signal; and a controller for providing a picture inversioncontrol signal to allow said video signal to be displayed invertedly athorizontal periods in which there is no video image being displayed onsaid liquid crystal display based on a result of comparing said detectedsync signal with a reference value and based on a picture inversioninput signal.
 2. A method for controlling picture inversion of a liquidcrystal display, comprising: detecting a sync signal from a video signalin response to a picture inversion input signal; comparing said detectedsync signal with a reference value; determining horizontal periods inwhich there is no video image being displayed on said liquid crystaldisplay in accordance with said comparison result; and providing apicture inversion control signal in accordance with a result of saiddetermination.